Pyroxenes in the system Mg2Si2O6-CaMgSi2O6 at high pressure |
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| Authors: | Takeshi Mori David H Green |
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| Institution: | 1. Research School of Earth Sciences, Australian National University, Canberra, A.C.T. Australia |
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| Abstract: | The enstatite-diopside solvus in the system Mg2Si2O6-CaMgSi2O6 has been experimentally determined within the pressure range 5–40 kbars and the temperature range 900–1500°C. Experiments involving reversal of the phase boundaries by unmixing from glass starting material and by reaction of pure clinoenstatite and diopside showed difficulty in achieving equilibration due to persistence of metastable, subcalcic clinopyroxene and to the sluggishness of reaction rate. The experimental data showed that the temperature dependence of the diopside limb is less than previously accepted. At 1500°C and 30 kbars subcalcic diopside found by Davis and Boyd (1966) is shown to be metastable with respect to enstatite and more calcic diopside of composition En42.3Di57.7. The solvus widens with increasing pressure between 5 and 40 kbars at 1200°C, but at 900°C the pressure effect on the solvus is very small. The stability relationships of the four pyroxenes, protoenstatite, enstatite, iron-free pigeonite and diopside are summarized, based on data from the literature and the present study. |
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